There is a new paper which is critical of the ERA-40 Reanalysis. This is an important issue as this data set has been used in long-term climate studies; e.g. see which has over 2000 citations in the peer-reviewed literature according to google scholar. The new paper is
Screen, James A., Ian Simmonds, 2011: Erroneous Arctic Temperature Trends in the ERA-40 Reanalysis: A Closer Look. J. Climate, 24, 2620–2627. doi: 10.1175/2010JCLI4054.1. (Roger Pielke Sr.)
